On a motion by Bernie Sanders, Democrats chose Hillary Clinton by acclamation as their presidential candidate. We are now left to choose between Clinton and Donald Trump to be the next U.S. president.

Never in my experience have two presidential candidates by their own words demonstrated their differences so clearly and starkly. Nor have those words carried such profound implications.

In hisacceptance speech at the Republican convention, Trump described the country as in flames at home and humiliated abroad. He assured voters that from the day of his inauguration he would by force of his superior will and intellect protect them from all threats—but revealed little about how he’d do it.

The next morning, Clinton introduced Senator Tim Kaine as her running mate. In her presentation, Clinton confronted Trump on what, for his true believers, is his greatest strength: his self-professed superhero power to save us from our many enemies. She then stressed the need to move beyond our differences and celebrated our potential as anation to come together as a diverse and vibrant community of the whole to create a nation of opportunity for all.

The stark contrast in the appeal of the Trump and Clinton messages reveals a deep conflict in our national psyche between our most primitive go-it-alone survival instincts and our human potential to organize as caring communities of the whole. It isas if Clinton and Trump are acting from and appealing to wholly different parts of our three-part human brain.

Our reptilian brain, the most primitive, is the seat of the individualistic autonomic behaviors basic to physical survival, such as breathing and our instinctive response to physical threat.

The limbic, or mammalian, brain rests on top of the reptilian brain. It isthe seat of our emotional consciousness, our ability to love, care, and bond with one another.

The third and largest brain, the neocortex, is the base of our capacity for reason, rational thought, and conscious, intelligent choice.

In the mature human adult, these three interconnected brains work in balanced relationship with one another. This gives us the ability to consciously and intelligently self-organize as a species: to function as healthy, caring families, communities, and members of a living Earth community.

The stark contrast in the appeal of the Trump and Clinton messages reveals a deep conflict in our national psyche.

Under conditions of extreme fear and uncertainty, even healthy adults can experience suppression of higher cognitive function and yield substantial control to the reptilian brain. Trump isa master at promoting and exploiting this regression to advance his quest for personal power. It is the basis of his political success.

The parade of horrors by which Trump plays to our reptilian brain consists largely of fictitious bogeymen. Ironically, a far greater real threat to the United States and the world would be an emotionally volatile and intellectually challenged American president using his mediaaccess to activate our reptilian brain while his finger rests on the nuclear button.

Clinton, in contrast to Trump, isappealing to our higher nature. Whatever her deficiencies, she recognizes that no single individual—not even the most qualified, let alone a politically inexperienced demagogue—can singlehandedly resolve complex issues like climate change and extreme inequality. The real issues of our time require that we work together as a community of the whole to deal intelligently with the very real issues of justice and sustainability.

Many of us distrust Clinton for her history of aligning with the corporate establishment in disregard of the larger community interest. Given the limited choices our badly flawed political system currently offers us, I believe our best hope for the just and sustainable future we must now live into being resides in a Clinton presidency held accountable by the powerful social movement that Bernie Sanders is building to liberate the Democratic Party from corporate establishment control.

More than any presidential election in recent memory, this election is less a contest between competing political ideologies than a contest between the primitive instincts of the reptilian brain and the potentials of our limbic and neocortical brains. It isa test of our intellectual, social, and emotional readiness as a nation to take the step to a new level of maturity and possibility.